The attachment in the sidebar becomes an editable workbook.

Our app adds a SumOffice link next to attachments in the Frappe form sidebar and puts a complete WOPI host behind it. The rights are the ones you already granted: reading needs the right to the file, writing needs write access to the document the file hangs on. Measured on Frappe / ERPNext 15.97.

What was measured

The round	A macro workbook and a document with five pictures: opened from the form, edited, saved back. VBA byte for byte, pictures byte for byte, the edit in place.
The refusals	Checked as well: unsigned and forged requests, corrupted tokens, wrong paths — each refused rather than tolerated.
Rights	Read follows the file permission; write follows write access to the parent document. Nothing new to administer.
What this does not say	The fixture workbook these rounds used asks Microsoft Excel to repair it on its own — so no silent-Excel claim here. See Nextcloud and Seafile.

Setting it up

# the editors, behind your TLS address
git clone https://github.com/SumOfficeApp/sumoffice-docker && cd sumoffice-docker/nextcloud
cp env.example .env    # PUBLIC_URL=https://office.example.com
docker compose up -d

# the app: sumoffice-docker, branch integrations, folder integrations/frappe
# bench get-app, bench --site … install-app sumoffice, then set the editor address

Evaluation is free with no time limit; production is the per-application license. The other systems we measured →

Then

Check my Excel file — what your workbooks rely on.
Tell us your Frappe version — 15 is measured.